The present invention relates generally to inkjet printing, and pertains more particularly to operation of an inkjet printing system as an ink supply nears exhaustion.
Hardcopy output devices, such as printers and fax machines, frequently make use of an inkjet printhead mounted within a carriage that is moved relative to a print medium, such as paper. Hardcopy devices of this sort are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devicesxe2x80x9d ,Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988). As the printhead is moved relative to the print medium, a control system selectively activates individual printing elements in the printhead to deposit or eject ink droplets onto the print medium to form printed output that may include images and text. Ink is provided to the printhead from a supply of ink. An inkjet hardcopy device typically uses several different color ink supplies, each with an associated printhead, to produce color print output. A typical set of color inks includes cyan, magenta, yellow, and black inks. During printing, drops of different ones of these inks may be deposited in the same or adjacent locations to form a range of colors. Further information as to the basics of inkjet printing technology are further disclosed in various articles in several editions of the Hewlett-Packard Journal[Vol. 36, No. 5 (May 1985), Vol.39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994)], incorporated herein by reference.
In order to ensure that the printed output is of high quality, it is critical that proper care of the printhead is taken during both operation and non-operation. If printing is attempted after the supply of ink has run out, the printing elements can be damaged from the entry of air into the printhead such that they will no longer operate properly when a new ink supply is provided. Similarly, care must be taken to ensure that moisture in the nozzles of the printing elements not dry out. When the printhead is not in operation, the nozzles are typically mechanically capped to retain moisture. During operation, when the nozzles are not capped but instead are exposed to air, the printing elements are periodically serviced, typically by ejecting drops of the ink into a spittoon, in order to keep the nozzles moist.
Since the color of the printed output may require that more of one certain color ink be used than of a different color ink, the ink supplies may become exhausted at different times. In hardcopy devices where the ink reservoir containing the supply of ink is integrally formed with the printhead in a print cartridge, both the ink reservoir and the printhead are replaced when the supply of ink is exhausted, so it does not matter if the printhead is damaged by attempting to print after the supply of ink is exhausted.
However, in other hardcopy devices where the ink reservoir is contained in an ink cartridge that is separate from and fluidically coupled to the printhead, the ink cartridge and the printhead are separately replaceable. While the ink cartridge is replaced when the supply of ink is exhausted, the printhead is generally not replaced until the end of its useful life, which typically is much longer than the life of a single ink supply. As a result, care must be taken to avoid printing once an ink supply is exhausted so as not to damage the corresponding printhead.
The amount of remaining ink in an ink supply can be automatically determined by the hardcopy device, and therefore it is possible for the hardcopy device to stop printing just before the supply of ink runs out, and prevent any further printing until the ink supply is replaced. While this behavior will prevent damage to the printhead, it is often otherwise undesirable. For example, the incoming fax data can""t be stored in certain types of fax machines; rather, it must be printed out at the time it is received or it will be lost. Also, in many printing devices a single ink cartridge may contain two or more color ink supplies in separate ink reservoirs, with a frequently-used combination including the cyan, magenta, and yellow inks in a tri-color ink cartridge. Since one of these color inks is likely to become exhausted while ink remains in the other reservoirs, requiring the user to replace a multi-color ink cartridge before printing can continue results in discarding the remaining supplies of ink for the non-exhausted colors.
Accordingly, it would be highly desirable to have a new and improved hardcopy printing method and system that allows the user to continue printing with the remaining color inks after one color ink has been exhausted without damaging the printhead associated with the exhausted ink supply.
In a preferred embodiment, the present invention provides a method of printing with an inkjet printer having a plurality of ink supplies. If the method detects that less than a predetermined reserve amount of ink remains in a depleted ink supply, then ink drops will be ejected from that depleted ink supply only during servicing operations. Since ink drops from non-depleted ink supplies will still be ejected during both printing operations and servicing operations, the user can advantageously continue printing after an ink supply has been depleted without damaging the printhead associated with the depleted ink supply.